Glucosylceramide synthase (GCS) is a key enzyme which catalyzes the initial glycosylation step in the biosynthesis of glucosylceramide-based glycosphingolipids (GSLs) namely via the transfer of glucose from UDP-glucose (UDP-Glc) to ceramide to form glucosylceramide. GCS is a transmembrane, type III integral protein localized in the cis/medial golgi. Glycosphingolipids (GSLs) are believed to be integral in many cell membrane events, including cellular interactions, signaling, and trafficking. Synthesis of GSL structures has been shown (Proc. Natl. Acad. Sci USA 1999, 96(16), 9142-9147) to be essential for embryonic development and for the differentiation of some tissues. Ceramide plays a central role in sphingolipid metabolism, and downregulation of GCS activity has been shown to have marked effects on the sphingolipid pattern with diminished expression of glycosphingolipids. Sphingolipids have a role in physiological as well as pathological cardiovascular conditions. In particular, sphingolipids and their regulating enzymes appear to play a role in adaptive responses to chronic hypoxia in the neonatal rat heart (Prostaglandins & Other Lipid Mediators 2005, 78(1-4), 249-263).
GCS inhibitors have been proposed for the treatment of a variety of diseases (see, for example, WO2005068426). Such diseases include glycolipid storage diseases (e.g., Tay Sachs, Sandhoffs, GM1 gangliosidosis, Niemanns-Pick, and Fabry diseases), diseases associated with glycolipid accumulation (e.g., Gaucher disease), diseases that cause renal hypertrophy or hyperplasia such as diabetic nephropathy, diseases that cause hyperglycemia or hyperinsulinemia, cancers in which glycolipid synthesis is abnormal, infectious diseases caused by organisms which use cell surface glycolipids as receptors, infectious diseases in which synthesis of glucosylceramide is essential or important, diseases in which excessive glycolipid synthesis occurs (e.g., atherosclerosis, polycystic kidney disease, and renal hypertrophy), neuronal disorders, neuronal injury, inflammatory diseases or disorders associated with macrophage recruitment and activation (e.g., rheumatoid arthritis, Crohn's disease, asthma and sepsis), pain (see WO2008011483—neuropathic pain, inflammatory pain, headache pain, somatic pain, visceral pain, referred pain), cognitive disorders (see WO2008/109286—agnosia; amnesia; aphasia; an apraxia; delirium; dementia including AIDS dementia complex, Binswanger's disease, dementia with Lewy Bodies, frontotemporal dementia, mild cognitive impairment, multi-infarct dementia, Pick's disease, semantic dementia, senile dementia, and vascular dementia; and learning disorders including Asperger's syndrome, attention deficit disorder, attention deficit hyperactivity disorder, autism, childhood disintegrative disorder, and Rett syndrome), neurodegenerative disorders (such as Alzheimer's disease, corticobasal degeneration, Creutzfeldt-Jacob disease, frontotemporal lobar degeneration, Huntington disease, multiple sclerosis, normal pressure hydrocephalus, organic chronic brain syndrome, Parkinson's disease, Pick disease, progressive supranuclear palsy, and senile dementia (Alzheimer type), glomerular disease, and diabetes mellitus and obesity (see WO 2006053043)). Renal hypertrophy induced by diabetes is associated with enhanced synthesis of glycosphingolipids such as glucosylceramide and ganglioside GM3, which accumulate in the kidney of rats (J. Clin. Invest. 1993, 91(3), 797).
It has been shown that overexpression of GCS is implicated in multi-drug resistance and disrupts ceramide-induced apoptosis. For example, Turzanski et al. (Experimental Hematology 2005, 33(1), 62-72) have shown that ceramide induces apoptosis in acute myeloid leukemia (AML) cells and that P-glycoprotein (p-gp) confers resistance to ceramide-induced apoptosis, with modulation of the ceramide-glucosylceramide pathway making a marked contribution to this resistance in TF-I cells. Thus, GCS inhibitors can be useful for treatment of proliferative disorders (such as cancer) by inducing apoptosis in diseased cells.
Sandhoff (or type 2 GM2 gangliosidosis) is caused by a deficiency in β-hexosaminidase A and B activity which leads to an accumulation of the ganglioside GM2 and other glycolipids causing damage to the central nervous system and eventually is lethal (PLoS One 2011, 6(6), e21758). Tay-Sachs disease (or GM2 gangliosidosis) is caused by a deficiency in β-hexosaminidase A which lead to an accumulation of gangliosides in the brain's nerve cells eventually leading to their premature death. Intravenous injection of the missing enzyme(s) is not a viable option as of the enzymes does cross the blood-brain barrier (Genetics in Medicine 2009, 1(6), 425). Glucosylceramide synthase is a key enzyme in the synthesis of glucosylceramide and other glycosphingolipids. Its inhibition can decrease the amount of the glycosphingolipids which accumulate in Sandhoff disease.
Fabry disease is caused by loss of activity of the lysosomal hydrolase α-galactosidase which leads to an accumulation of glycosphingolipids (particularly globotriaosylceramide) causing pain, renal disease and failure, cerebral vascular disease, and myocardial infarction (Kidney International 2000, 57, 446). One treatment strategy is to provide the defective enzyme to the patient; however, enzyme replacement therapy can only slow the progression of the disease and is not a cure. An alternative or complementary strategy is one where glucosylceramide synthase, a key enzyme in the synthesis of glycosphingolipids, is inhibited with a small molecule thus decreasing the amount of globotriaosylceramide and other glucosylceramide-based lipids that need to be broken down by hydrolase α-galactosidase.
Gaucher disease is caused by a defect in the enzyme lysosomal glucocerebrosidase which is responsible for catalyzing the breakdown of glucosylceramide which then accumulates in tissues of affected people (J. Org. Chem. 2007, 72(4), 1088) causing liver malfunction, skeletal disorders, painful bone lesions, hypersplenism, pancytopenia, and neurological symptoms (convulsions, hypertonia, mental retardation, apnea, dementia, and ocular muscle apraxia). One treatment strategy is to provide the defective enzyme to the patient; however, enzyme replacement therapy is not suitable for all patients and does not address the neurological manifestations of the disease for those with type 2 and type 3. An alternative or complementary strategy is one where glucosylceramide synthase is inhibited with small molecules thus decreasing the amount of glucosylceramide that needs to be broken down by glucocerebrosidase.
Nonalcoholic fatty liver disease (NALD) is a disease where fat accumulates in the liver of people who drink little or no alcohol and results in inflammation and scarring of the liver which can progress to liver failure. Inhibition of glucosylceramide synthase in ob/ob mice lowered glucose levels, lowered liver/body weight ratio, decreased the accumulation of triglycerides, and prevented and reversed steatosis (Hepatology 2009, 50(1), 85-93). Thus GCS inhibitors are useful for the prevention and treatment of NALD.
Polycystic kidney disease (PKD) is a genetic disease characterized by noncancerous cysts which are filled with fluid and cause the kidneys to enlarge which can result in a decrease in quality of life (e.g., headaches, high blood pressure, back and side pain, colon problems, mitral valve prolapsed, and kidney stones) and can be life-threatening (e.g., kidney failure, aneurysm in the brain, and high blood pressure which can lead to heart disease and stroke). PKD can also damage the liver, spleen, pancreas, vasculature, testes, seminal vesicles, and intestines. Glucosylceramide and ganglioside GM3 levels in the kidney are higher than in normal tissue (Nat Med 2010, 16(7), 788). Thus, blocking the synthesis of glucosylceramide with an inhibitor of GCS can be useful in the treatment of PKD to reduce new cyst formation (partial or complete inhibition of cystogenesis), reduce cyst mass, reduce the size and number of cysts, and/or reduce the severity of the symptoms associated. All current treatments for PKD address symptoms and do not treat the underlying cause of the disease (Nat Med 2010, 16(7), 788).